My horse’s leg is swollen : Lymphangitis

Lymphangitis in horses consisits in a very rapid swelling of a limb, due to an inflammation (suffix « itis » of the lymph vessels. This complaint most often affects the hind limbs and is usually unilateral (only one limb is affected).

The swelling can be impressive, as the lower part of the limb sometimes swells to 2 or 3 times its normal size. The swelling can spread quite high on the limb : most often up to the hock, sometimes as high as the stifle, and even as far as the teats. When the skin is pressed with a finger, the mark of the finger remains visible for a few moments once the finger has been removed. This shows the presence of oedema. There may also sometimes be weeping of the skin (when touched it feels squidgy).

The oedema makes the skin very tense, it is painful to the touch, and frequently causes marked lameness. These local symptoms may be associated to general symptoms such as :

• Hyperthermia (T > 38,5°C) ;
• Loss of appetite, general lethargy, sweating, trembling, increase in breathing rate which are linked to the high temperature and the pain.

When there is major swelling and it is not addressed immediately, the limb can remain deformed,  a thickening of the skin and chronic lameness can also be observed. Chronic lymphangitis can also disrupt the growth of the horn, as it disrupts the function of the coronet. It is also frequently a recurring complaint.

Lymphangitis is typically caused by a bacterial infection of a wound, or evenjust an insect bite, or grazed skin.

The lymph system is composed of :

• Lymph ducts;
• Lymph nodes (or ganglions) ;
• But also of other lymph organs (e.g the spleen).

Lymph travels through the lymph ducts to the lymph nodes. The lymph system enables among other :

• Drainage of excess liquid in the tissues and plays a role in detoxifying the body ;
• Circulation of the white blood cells, which protect the organism from aggressions from ouside organisms such as bacteria for example.

During a bout of lymphangitis, the multiplication of bacteria goes above the functional capacities of the lymph nodes which can then in turn become infected. The subsequent inflammation of the lymph vessels impedes circulation of lymph liquid, and the drainage of inflammatory liquids in the limb which are the causes of the oedema. Unlike the blood system, the lymph system does not have an organ which acts as a pump (the heart).

When lymphangitis is suspected the veterinarian needs to intervene quickly. The diagnosis is mainly based on the clinical symptoms, and the acute character of the swelling, characteristic to the condition. The vet will look for the entry point of the bacteria. Sometimes the wound is so minor, that even after careful examination of the skin the entry point cannot be found.

Prompt treatment is essential to avoid the condition becoming chronic and leading to a permanent deformation of the limb, to relieve the pain, and to restore the horse’s appetite if necessary.

Treatment is based on administering:

• Antibiotics to fight the infection;
• Non steroid anti-inflammatories and/or medication for oedema to relieve the pain and reduce inflammation and the oedema.

For chronic cases, massaging the limb regularly can help in draining excess fluids. Keeping a close eye on horses presenting chronic forms or susceptible to recurring bouts is vital so as to intervene as soon as possible.